Acute lung injury (ALl) is a common response to a variety of insults, including endotoxemia, infectious pneumonia, toxic gas inhalation, and aspiration. Because neutrophilic inflammation is a prominent and universal feature of ALl, the neutrophil is thought to play a central role in mediating lung injury. Even so, its exact contribution is still controversial. For instance, even the relationship of neutrophil activation to the development of lung tissue injury remains unclear. Glycolysis is the major energy source for key neutrophil functions; increased glucose uptake by the neutrophil in support of glycolysis is a marker of neutrophil activation. Based on this property, we have shown that the pulmonary uptake of the glucose analog [18F]fluorodeoxyglucose (FDG) with positron emission tomography (PET) accurately quantifies lung neutrophil activation in animal models of lung injury and infection, providing a basis for using this imaging strategy to test the hypothesis that differences in the magnitude and/or duration (i.e. the "kinetics") of neutrophil activation determine the extent to which neutrophils contribute to lung tissue injury. Since other metabolically active tissues (and inflammatory cells) can also take up [18F]FDG, a complementary imaging strategy that is neutrophil-specific is needed to properly interpret the FDG-PET imaging signal. To address this need, during, the R21 Phase of this proposal, we intend to generate a transgenic mouse expressing a mutant form of the Herpes simplex virus-1 thymidine kinase) under the control of a neutrophil-specific (cathepsin G) promoter as an imaging reporter gene. The product of this transgene can trap tracers such as 9-(4-[18F]-fluoro-3-hydroxymethylbutyl)guanine ([18F]FHBG) in those cells expressing the reporter protein. The tissue accumulation of the tracer can be measured non-invasively with PET. Then, in the R33 Phase, we will use imaging with both [18F]FHBG and [18F]FDG to test our hypothesis in knockout mice in which the neutrophilic response to ALl is abnormal. In addition to learning more about the biology of ALl, the development of this transgenic mouse should be viewed as a new imaging tool, broadly applicable to various diseases characterized by neutrophilic inflammation and tissue damage, including arthritis, inflammatory bowel disease, and ischemia-reperfusion injuries.